1. Field of the Invention
The present invention relates to a fuel cell including a cell unit formed by stacking an electrolyte electrode assembly between a first separator and a second separator. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between said electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, an anode and a cathode each including an electrode catalyst layer and a porous carbon are provided on both sides of the solid polymer electrolyte membrane to form a membrane electrode assembly (electrolyte electrode assembly). The membrane electrode assembly is sandwiched between separators (bipolar plates) to form a unit cell. In use, normally a predetermined number of unit cells are stacked together to form a fuel cell stack.
In general, the fuel cell adopts so called internal manifold structure in which supply passages and discharge passages extending through the separators in the stacking direction are provided in the fuel cell. A fuel gas, an oxygen-containing gas, and a coolant are supplied to a fuel gas flow field, an oxygen-containing gas flow field, and a coolant flow field through the respective supply passages, and thereafter, the fuel gas, the oxygen-containing gas, and the coolant are discharged from the fuel gas flow field, the oxygen-containing gas flow field, and the coolant flow field through the respective discharge passages.
For example, in Japanese Laid-Open Patent Publication No. 2001-102072, as shown in FIG. 10, an electrode unit 2 is stacked on a separator 1A, a separator 1B is stacked on the electrode unit 2, another electrode unit 2 is stacked on the separator 1B, and a separator 1C is stacked on the electrode unit 2. The electrode unit 2 is formed by joining a solid polymer electrolyte membrane 2a between an oxygen-containing gas electrode 2b and a fuel electrode 2c. A gasket 3 is formed integrally with an outer end of each of the solid polymer electrolyte membrane 2a by injection molding.
Each of the separators 1A, 1B has a fuel gas supply channel 4a on a surface facing the fuel electrode 2c, and each of the separators 1B, 1c has an air supply channel 4b on a surface facing the oxygen-containing gas electrode 2b. A coolant water supply channel 4c is provided between the separators 1A, 1C.
An air supply hole (fuel gas supply hole, coolant water supply hole) 5a and an air discharge hole (a fuel gas discharge hole, a coolant water discharge hole) 5b extend through the separators 1A, 1B, and 1C and the gaskets 3 in the stacking direction, and the air supply hole 5a, the air discharge hole 5b are connected to the air supply channels 4b. On both surfaces of the gaskets 3, bead-like protrusions 6 are provided for preventing leakage of the fuel gas, the air, and the coolant water.
However, in order to reliably prevent leakage of the fuel gas, the air, and the coolant water, the height of the protrusions 6 (dimension in the stacking direction) need to be large. Thus, the gaskets 3 are significantly thick, and it is not possible to reduce the overall thickness (size) of the fuel cell.
In particular, in a fuel cell stack mounted in a vehicle, since several hundreds of unit cells are stacked together, reduction in the thickness is desired. For this reason, the above fuel cell cannot be adopted for this type of the fuel cell stack.